Traditionally, inkjet printing is accomplished by one of two technologies referred to as “drop-on-demand” and “continuous” inkjet printing. In both, liquid, such as ink, is fed through channels formed in a print head. Each channel includes a nozzle from which droplets are selectively extruded and deposited upon a recording surface.
Drop on demand printing only provides drops (often referred to a “print drops”) for impact upon a print media. Selective activation of an actuator causes the formation and ejection of a drop that strikes the print media. The formation of printed images is achieved by controlling the individual formation of drops. Typically, one of two types of actuators is used in drop on demand printing—heat actuators and piezoelectric actuators. With heat actuators, a heater, placed at a convenient location adjacent to the nozzle, heats the ink. This causes a quantity of ink to phase change into a gaseous steam bubble that raises the internal ink pressure sufficiently for an ink droplet to be expelled. With piezoelectric actuators, an electric field is applied to a piezoelectric material possessing properties causing a wall of a liquid chamber adjacent to a nozzle to be displaced, thereby producing a pumping action that causes an ink droplet to be expelled.
Continuous inkjet printing uses a pressurized liquid source that produces a stream of drops some of which are selected to contact a print media (often referred to a “print drops”) while other are selected to be collected and either recycled or discarded (often referred to as “non-print drops”). For example, when no print is desired, the drops are deflected into a capturing mechanism (commonly referred to as a catcher, interceptor, or gutter) and either recycled or discarded. When printing is desired, the drops are not deflected and allowed to strike a print media. Alternatively, deflected drops can be allowed to strike the print media, while non-deflected drops are collected in the capturing mechanism.
Printing systems that combine aspects of drop on demand printing and continuous printing are also known. These systems, often referred to a flow through liquid drop dispensers, provide increased drop ejection frequency when compared to drop on demand printing systems without the complexity of continuous printing systems. As such, there is an ongoing effort to increase the reliability and performance of flow through liquid drop dispensers.